Manufacture of rubberlike materials



Patented Nov. 23, 1948 -MANUFAGTURE F RUBBERLIKE MATERIALS Cecil Albert Curtis, Manchester, a-n'd'Douglas Sandford Stephens, Cheadle, England NoiDrawing. Application August 1947, Serial? In-Great Britain September 4,

Section 1, Public Law 690. August 8,1946

Patent expires April l l', 1964 a Claims. (01. 260-,-67

This invention relates to thev manufacture of rubber-like materials containing? sulphur; It is known that plastic materials can be" madeby reaction between certainaa'ldehydes and alkaline polysulphides; see;. for: example, United States patent specifications Nos. 2,039,206,. 2,255,228, 2,012,347 and.l.890,19l=. However, bythese'known processes, products areobtained which rapidly become hard? and brittle-,, and: which when compounded; and subjected to a. curing treatment, yield products which do'noti eX-hibitt-he properties of resilience and tensile strength required in a rubber-like product.

It is anxobjtect of. the presentziinventi'on-s. to make rubber-likematerialswhich. doznot: harden on: storageand which; cambe compounded and cured to: yield. resilient: rubb'er like" products of good tensile: strength.

According: to the :present" invention; rubber-like material's are made by reacting. an aliphatic. thioaldehydewwithsa quantity of. elementary: sulphur ranging from: to 12: atomic proportions per atomic proportion: of; combined? sulphur in the thioaldehyde imam aqueous mediumaat av temperatureranging from" 80 C. to,-the=bo-iling point while-maintaining the pH value? of the. aqueous medium. between; 1.5; and 1.0? throughout the reaction.

As the aliphatic-tthioaldehydei there. may be used thioformaldehyde or thioacetaldehyde; and the thioaldehydes may be used as such or in the form of the products obtained by the action of hydrogen sulphide: on-the: corresponding aldehyde. By the act-1on1of hydrogerr-sulph de on i the aldehyde the formationciproductsrof: a polymeric nature: isunavoidabler. but for theipurposes ofthis invention. it; is desirable to; keep; the proportion of such' products as low as: possible. This/may be achieved. by conducting; the reaction v between hydrogen. sulphide and. the aldehyde under sub:- stantially neutraltoonditions, at". a; low tempera,- ture and: in a shortlperiod ofl reaction.

The: preparation: of the"- thioaldehyde; and: the reaction thereof with-elementary sulphur in accordance with the invention may be conducted as two separate stages; and the reaction mixture obtained; in the first stage may be. used, directly for the. reactionz-withsulphun. Alternatively, the preparation of,theathioaldehyderand thereaction with sulphur may be: carried oute'i-ma isingle? operationr It is necessaryzto' conductwthei reaction: Ofrthe thioaldehydeawith elementary sulphur. at a.- pH value. ranging fromlhhto l0, because:=atpH values outside these limits materials are obtained which, when cured, do not yield resilient rubberlike products of good tensile strength. The desiredpH value may bemaintained by adding to the reaction mixture'a substance of alkaline reaction, for example, trisodium phosphate, borax or'zinc oxide, ora substance ofaci'd reaction, for example, stearic acid, potassium dihydrogen phosphate or sulphuric acid.

While the. proportion of elementary sulphur used in the reaction with the thioaldehyde may rangeirom" to*12atomic proportions per atomic proportion of combined sulphur in the thioaldehyde, especially advantageous products are obtained by: using 1-3 atomic proportions of elementary sulphur.

The products of the reaction between the thinaldehydes and elementary sulphur (hereinafter referred to as primary products) are elastic, soft and plastic materials which are insoluble. in mineral oils and in. the normal rubber solvents, except. carbondisulphide. These primary products may also be obtained in the form of latexlike compositions by'conductine the reaction with elementary: sulphur in the presence of a substance, such as magnesium: oxide,- which inhibits the agglomeration of the product. Latex-like compositions may al=o be obtained by subsequently emulsifying the primary products.

The primary products, with orwithout previous purification: may-becompounded and cured in a manner similar to that of natural or synthetic rubber.

According to afurther'feature ofi th'einvention the primary products are converted into seconde ary products, which are elastic materials of remarkable t'ouehnessand strength; by treatment with an acid: condensing agent, such as sulphuric acid or aluminium chloride. The primaryproducts and the SBCOHdaTX'IJrOdIIGtSI are, undernormal conditions, insoluble in. mineral oils and in the usual rubber solvents, except carbon dissulphid'e, in which they aretslightly soluble. They also have" an. outstanding resistance to acids, suchzas strong mineral acids and even oxidising acids like nitric acid and chromic acid.

The primary andsecondaryproduct's alone or in admixture withonetanother can be compounded and curedribythemselves or together withnatural or synthetic.rubbers,= with rubber substitutes such as factice, with sulphur or withnatural'or artificial resins; Thet compounding andcuring ofthe primary and/or secondary products may also :be conducted'with the" addition of afllling material; and'suchafilling material'maybe added at; an earlier: stage in; the. manufacture; for exheated to 80 C.

be cured by an open steam cure or a wet cureor by dry heat. I

The rubber-like products obtained by compounding and curing the primary and/or secondary products are of good resilience and tensile strength.

The following examples illustrate the invention, the parts being by weight:

Example 1 164 parts of formaldehyde solution of 40 per cent. strength are neutralised with borax t-apH of 7. Hydrogen sulphide is then passed through the solution at a temperature of -20 C. until the specific gravity is 1.13. Instead of pas-sing thehydrogen sulphide through the solution, the gas may be brought into intimate contact with the solution by exposing a large surface of the solution to the gas, for example, by allowing the formaldehyde solution to percolate downwards through an absorption tower filled with Raschig rings and passing a current of hydrogen sulphide through the tower in the opposite direction. The desired degree of absorption may be attained either by recirculating the solution through the tower or by passing the solution through a succession of towers. The solution takes up 42 parts of hydrogen sulphide, so that it contains 19 per cent. of combined sulphur. Its pH value is 6.5.

There are then added to the resulting solution '90 parts of finely ground sulphur and parts of borax. The mixture is heated to the boil and then has a pH value of 8.6. It is refluxed in a vessel provided with stirring means until the aqueous layer has become clear and the reaction is at an end. The pH value becomes progressively lower during the reaction and is 8.0 when the endpoint is reached. The product is then isolated and washed free from mother liquor. It is an elastic greenish-yellow plastic. 145 parts of the final product are obtained which corresponds to an addition of 2.2 atomic proportions of sulphur per atomic proportion of combined sulphur in the solution treated.

Example 2 150 parts of the product obtained as described in Example 1 are heated to 100 C. in 100 parts of sulphuric acid of 97 per cent. strength, and the mixture is stirred for hour at this temperature. The plastic product is isolated and washed free from acid. It then forms a tough and elastic rubber-like material.

Example 3 109 parts of formaldehyde solution of per cent. strength are neutralised with borax to a pH of 7, and are then treated with hydrogen sulphide at a temperature of l5-20 C. in the manner described in Example 1. 81 parts of the solution so obtained, which contains 19 per cent. of combined sulphur, are mixed in a stirring pan with 36 parts of ground sulphur and rapidly 6 parts of trisodium phosphate are added and the mixture is brought to the boil under reflux as rapidly as possible, the pH value being 9.8 when the boil is reached. Boiling is continued for 30 minutes, during which the pH value .drops pared as described 4 to 8.6. After settling, the clear aqueous solution is decanted, and the soft product washed with hotwater until it is free from the odour of formaldehyde. 58 parts of the product are obtained. The same yield is obtained when working in substantially neutral solution, 1. e., without any addition of a pH regulator, the product in this case being somewhat softer. The pH value at the end of the neutral reaction is 6.3.

Example 4 660 parts of formaldehyde solution of 4!) per cent strength are neutralised with borax to pH 7 Hydrogen sulphide is then passed through the liquid whilst stirring at a temperature of 15-18 C. until saturation point is reached. The solution containing 19 per cent. of combined sulphur is filtered and 180 parts of ground sulphur and 60 parts of zinc oxide added to the filtrate. The mixture is then refluxed for 30 minutes with strong agitation, the pH being 7.4 when the boil is reached and. dropping to 6.9 at the end of the refluxing.

A cream coloured suspension is thus obtained, which is then washed by decantation until free from formaldehyde. The product is then isolated by filtration with a yield of 463 parts of a soft sticky mass. By mixing this product with an emulsifying agent, such as triethanolamineoleate, and an aqueous medium, a stable latexlike suspension is obtained.

Example 5 Hydrogen sulphide is passed through freshly prepared acetaldehyde at a temperature of 15 C. The resulting mixture of acetaldehyde vapour and hydrogen sulphide is passed over solid trisodium phosphate which is maintained at a temperature of 7580 C;, and the reaction prodnot containing 18.3 per cent. of combined sulphur is condensed'by means of a cooling mixture.

345 parts of the liquid reaction product so obtained are allowed to react'with 125 parts of ground sulphur in 290 parts of water and 24 parts of zinc oxide in a closed enamelled vessel under slight pressure for 1% hours at the temperature of the boiling water bath, the pH value being approximately 7. 290 parts of a soft elastic product are obtained having a greenish grey colour.

' Example 6' 164 parts of formaldehyde solution are neutralized with borax to pH 7 and saturated with hydrogen sulphide in'the manner described in Example 1. parts of finely ground sulphur and 0.75 part of stearic acid are added and the mixture is refluxed for 3 hours. The pH at the beginning of the reaction is 5.5, and drops to 4.76 at the end. Afterwashing out the impurities by decantation the end product is dried by heating to 60 C. under vacuum. The dry weight is 139 parts. The product is soft and elastic and has a greenish-yellow colour.

Example '7 818 parts of thioformaldehyde solution prein Example 3 are heated together with 360 parts of sulphur, 60 parts of disodium phosphate and 60 parts of powdered white factice for 2 hours under reflux, the pH value being 8.15 when the boil is reached and drops to 7.0 at the end of the reaction. 640 parts of a yellow opaque and elastic product are obtallied.

. s ee le N 6 Per sc Oxide d P a weer nesium oxid e. streamed to a mixture its part at the thioiormaldehydesolution, obtained as del0 ans nelv ia i a creamy, latex-like product temp 9 100 parts of the productobtained as described in Example 1, 2, 3, or '7 are compounded with 0.1 part of diphenyl-guanidine, 0.35 part of dibenzthiazole-l:1-disulphide, 0.5 part stearic acid, and 60 parts of carbon and 10 parts of zinc oxide, by means of moderately heated rollers. The sheets so obtained are cured in an open steam cure by heating gradually, that is to say in about minutes. to 135 C. and maintaining this temperature and the corresponding steam pressure for 1 hour. It is of advantage to cool down under pressure in the vulcaniser. moulded into articles of various shapes by heat and pressure, temperatures of 110-120 C. and pressures of 55-110 lbs. per square inch being suitable. Non-porous rubber-like articles are thus obtained.

Example 10 100 parts of the product obtained as described in Example 6 are compounded with 60 parts of carbon and 10 parts of zinc a dry heat cure in a press for 1 hour at a temperature of 135 C. and a pressure of 930 lbs. per square inch. The following table shows the effect of the cure:

Tensile strength at break, Elongation Shore lbs. per at break hardsquare ness inch Freshly compounded sheets. 80 700 Nil Cured sheets 530 180 82/78 The cured product which is non-porous can be remoulded to any desired shape as described in Example 9.

Example 11 Material compounded as described in Example 9, but not cured, is rolled into very thin sheets, and the latter are calendered on to textile material at a temperature of 110 C. During the calendaring, curing takes place and impermeable materials resembling oil-cloth are produced.

Example 12 Sheets compounded as described in Example 9 but not cured, are subjected to a wet cure by wra ping them into cotton cloth, and curing at 135 C. in water which is heated indirectly by a steam coil, the pressure inside the vessel rising automatically. Cooling is carried out by gradually replacing the hot water by cold water, whilst maintaining the pressure inside the vessel at about lbs. per square inch. A non-porous material similar to that of Example 9 is obtained.

Example 13 The mixture described in Example 9 is compounded on moderately heated rollers, with the The cured product may be oxide by means of rollers, and the resulting sheets are subjected to 6 additiomoli 1 0 parts of sulphur powderduring the compounding operatiorn The resulting material is. cured in the manner described in Example 9, 10 or. 12, and elastic materials of leatherlike appearance are obtained.

Eagample 14 e i isn eti sm mb r 19 m and now abandoned.

We claim:

1. A process for making rubber-like materials which comprises reacting an aliphatic thioaldehyde with a quantity of elementary sulphur ranging from to 12 atomic proportions per atomic proportion of combined sulphur in the thioaldehyde in an aqueous medium at a temperature ranging from C. to the boiling point while maintaining the aqueous medium at a pH value ranging from 1.5 to 10 throughout the reaction.

2. A process for making rubber-like materials which comprises reacting an aliphatic thioaldehyde with a quantity of elementary sulphur ranging from 1 to 3 atomic proportions per atomic proportion of combined sulphur in the thioaldehyde in an aqueous medium at a temperature ranging from 80 C. to the boiling point while maintaining the aqueous medium at a pH value ranging from 1.5 to 10 throughout the reaction.

3. A process for making rubber-like materials which comprises reacting thioiormaldehyde with a quantity of elementary sulphur ranging from A; to 12 atomic proportions per atomic proportion of combined sulphur in the thioaldehyde in an aqueous medium at a temperature ranging from 80 C. to the boiling point while maintaining the aqueous medium at a pH value ranging from 1.5 to 10 throughout the reaction.

4. A process as claimed in claim 3, wherein the quantity of elementary sulphur ranges from 1 to 3 atomic proportions per atomic proportion of combined sulphur in the thioiormaldehyde.

5. A process for making rubber-like materials which comprises reacting thioacetaldehyde with a quantity of elementary sulphur ranging from to 12 atomic proportions per atomic proportion of combined sulphur in the thioaldehyde in an aqueous medium at a temperature ranging from 80 C. to the boiling point while maintaining the aqueous medium at a pH value ranging from 1.5 to 10 throughout the reaction.

6. A process as claimed in claim 5, wherein the quantity of elementary sulphur ranges from 1 to 3 atomic proportions per atomic proportion of combined sulphur in the thioacetaldehyde.

7. A process for making rubber-like materials which comprises reacting an aliphatic thioaldehyde with a quantity of elementary sulphur ranging from to 12 atomic proportions per atomic proportion of combined sulphur in the thioaldehyde in an aqueous medium at a temperature ranging from 80 C. to the boiling point while maintaining the aqueous medium at a pH value ranging from 1.5 to 10 throughout the reaction, isolating the resulting rubber-like material from the reaction mixture, and subjecting the isolated material to further condensation by means of an acid condensing agent.

8. A process for making cured rubber-like materials, which comprises reacting an aliphatic thioaldehyde with a quantity of elementary sulphur ranging from A; to 12 atomic proportions per atomic proportion of combined sulphur in the thioaldehyde in an aqueous medium at a temperature ranging from 80 C. to the boiling point while maintaining the aqueous medium at a pH value ranging from 1.5 to 10 throughout the reaction, isolating the resulting rubber-like ma- .terial from the reaction'mixture, and compounding and curing the isolated material.

9. A process for making cured rubber-like materials, which comprises reacting an aliphatic thioaldehyde with a quantity of elementary sulphur ranging from A to -12 atomic proportions per atomic proportion of combined sulphur in the thioaldehyde in an aqueous medium at a temperature ranging from 80 C. to the boiling point while maintaining the aqueous medium at a pH value ranging from 1.5 to 10 throughout the reaction, isolating the resulting rubber-like material from the reaction mixture, subjecting the isolated material to further condensation by means of an acid condensing agent, and compounding and curing the resulting further condensed rubber-like material.

CECIL ALBERT CURTIS.

DOUGLAS SANDFORD STEPHENS.

No references cited. 

